Turbo blood pump

ABSTRACT

A turbo blood pump includes a housing, an impeller rotatably disposed in a pumping chamber, bearings for rotatably supporting the impeller, a rotor provided outside the housing and rotationally driven by a motor, driven magnets mounted on the impeller, and driving magnets mounted on the rotor. The driven magnets and the driving magnets face each other via a wall of the housing to form magnetic coupling. The driven magnets and the driving magnets are arranged so that a direction of the magnetic coupling inclines with respect to a rotation axis of the impeller. The pump ensures sufficiently strong magnetic coupling between an impeller and a rotor and effects reduced load on a lower bearing supporting the impeller and little risk of hemolysis and blood stagnation.

FIELD OF THE INVENTION

[0001] The present invention relates to a blood pump for transferringblood. In particular, the present invention relates to a turbo bloodpump that causes blood to flow by the rotation of an impeller.

BACKGROUND OF THE INVENTION

[0002] Blood pumps are indispensable for conducting extracorporealcirculation by means of artificial heart lung apparatuses or the like.The blood pumps mainly used at present are turbo blood pumps. The turboblood pump has the following structure: A housing with a pumping chamberformed inside is provided with an inlet port for introducing bloodthereinto at its center and an outlet port for discharging bloodtherefrom on its periphery. An impeller is disposed in the pumpingchamber, the rotation of which gives blood a centrifugal force or adriving force in the axial or oblique direction, thereby causing theblood to flow.

[0003] To rotate the impeller by a motor, the pump needs a mechanism fortransmitting the rotation of the motor disposed outside the housing tothe impeller disposed inside the housing. As an example of suchtransmission mechanism, the structure is known in which the housing isprovided with an aperture so that the rotary shaft of the motorpenetrates the housing therethrough to be connected to the impeller witha shaft seal separating the inside and outside of the housing. In thiscase, however, the heat generated at the shaft seal may bring aboutproblems such as damage to blood and the formation of thrombus. Inaddition, the shaft seal cannot completely separate the inside andoutside of the housing, thereby allowing the invasion of bacteria etc.

[0004] In order to solve the above problems, the use of magneticcoupling as a means of connecting an impeller and a motor has beendevised. The use of the magnetic coupling can eliminate the necessity ofthe structure in which a drive shaft of the motor for transmittingrotation to the impeller penetrates the wall of the housing.

[0005] In the general structure for inducing magnetic coupling, magnetsare mounted on the impeller and on the rotor provided outside thehousing, and the magnets on the impeller and those on the rotor arearranged in close proximity. When the rotor is rotated by a motor, theimpeller rotates following the rotation of the rotor through themagnetic attraction force.

[0006] JP 9(1997)-313600 A discloses an example of the turbo blood pumpemploying the magnetic coupling. In this example, magnets are mounted onthe lower surface of the impeller and on the upper surface of a rotor.Accordingly, the magnets on the impeller and those on the rotor faceeach other in the vertical direction via the wall of the housing, andthe rotation of the rotor is transmitted to the impeller through themagnetic attraction force acting in the vertical direction. In the bloodpump of this type, since the attraction force caused by the magnets actsvertically, the lower side bearing for rotatably supporting the impellermainly is exposed to the load. Therefore, an attempt to obtain asufficiently strong magnetic coupling force increases abrasion of thelower side bearing, which may result in degraded pump performance and anadverse effect on the life of the pump.

[0007] Further, as an another example of magnetic coupling, theinventors of the present invention have studied the structure in whichmagnets on an impeller and those on a rotor are arranged so as to faceeach other in the radial direction. FIG. 3 shows an example of thisstructure. In FIG. 3, reference numeral 21 denotes a housing, whichincludes an inlet port 21 a and an outlet port (not shown in thedrawing). In a pumping chamber 22 provided inside the housing 21, animpeller 23 is disposed. The impeller 23 is rotatably supported by anupper bearing 24 and a lower bearing 25. In a recess 21 b formed at thecenter portion of the lower part of the housing 21, a rotor 26 isdisposed. Although it is not shown in the drawing, the rotor 26 isrotationally driven by a motor to which it is connected. Driven magnets27 are mounted on the lower part of the impeller 23 so as to be placedinside the side wall of the recess 21 b of the housing 21. On the otherhand, driving magnets 28 are mounted on the rotor 26 so as to be placedoutside the side wall of the recess 21 b. Accordingly, the rotation ofthe rotor 26 is transmitted to the impeller 23 through the magneticattraction force acting in the radial direction between the drivenmagnets 27 and the driving magnets 28.

[0008] In the blood pump of this type, to sufficiently increase an areaof the portions where the driven magnets 27 and the driving magnets 28face each other, respectively, for the purpose of obtaining asufficiently strong magnetic coupling force, both the magnets need tohave a sufficient length in the axial direction of the impeller 23.Accordingly, the area B of the outermost peripheral surface 23 a of theimpeller 23 is increased. Since the outermost peripheral surface 23 ahas the greatest peripheral velocity, an increase in this area means anincrease in the shear stresses on blood, which may increase the chancesof blood damage (hemolysis). In addition, since blood stagnationportions 29 are liable to be formed in spaces between the portions onwhich the driven magnets 27 are mounted and the side wall of the recess21 b, an increase in the volume of these spaces is not preferablebecause it increases the chances of thrombus formation.

SUMMARY OF THE INVENTION

[0009] Therefore, with the foregoing in mind, it is an object of thepresent invention to provide a turbo blood pump that ensuressufficiently strong magnetic coupling between an impeller and a rotordisposed outside a housing, prevents the load concentration to a lowerbearing supporting the impeller, and suffers little risk of hemolysisand the formation of blood stagnation portions.

[0010] A turbo blood pump according to the present invention includes ahousing having a pumping chamber, an inlet port, and an outlet port; animpeller rotatably disposed in the pumping chamber; bearings forrotatably supporting the impeller; a rotor provided outside the housingand rotationally driven by a motor; driven magnets mounted on theimpeller; and driving magnets mounted on the rotor, the driven magnetsand the driving magnets facing each other via a wall of the housing toform magnetic coupling, rotation of the rotor being transmitted to theimpeller through the magnetic coupling. The driven magnets and thedriving magnets are arranged so that a direction of the magneticcoupling, which is defined based on an attraction force acting betweenthe driven magnets and the driving magnets, inclines with respect to arotation axis of the impeller.

[0011] According to the turbo blood pump of the invention, since thedirection of the magnetic coupling inclines, the load applied downwardto the lower bearing, which is caused by the magnetic attraction forcebetween the impeller and the rotor, can be reduced. Thus, the magneticcoupling can be made sufficiently strong. Moreover, since the drivenmagnets and the driving magnets are disposed on oblique surfaces, anarea of the portions where the driven magnets and the driving magnetsface each other, respectively, can be increased easily withoutincreasing the axial size of the impeller. Therefore, an area of theportions coming into contact with blood at high peripheral velocity isdecreased, thereby reducing the chances of hemolysis. In addition, bloodstagnation portions also are made smaller, thereby reducing theformation of thrombus.

[0012] In the turbo blood pump according to the present invention, it ispreferable that an angle at which the direction of the magnetic couplinginclines with respect to the rotation axis of the impeller is in a rangeof 30°±15°.

[0013] Further, it is also preferable that the number of the drivenmagnets and the number of the driving magnets are in a range of 4 to 8,respectively, and the driven magnets and the driving magnets arearranged at substantially uniform intervals on circumferences centeredon the rotational axis of the impeller, respectively.

[0014] Furthermore, it is also preferable that the wall of the housingbetween the driven magnets and the driving magnets inclines at apredetermined angle with respect to the rotation axis of the impeller,oblique surfaces inclining along the wall are formed in a lower part ofthe impeller and an upper part of the rotor, respectively, and thedriven magnets and the driving magnets are arranged on the obliquesurfaces, respectively, so as to face each other in parallel.

[0015] In the turbo blood pump of the invention, the oblique surface inthe upper part of the rotor preferably protrudes toward the housing soas to form a convex shape.

[0016] In the turbo blood pump of the invention, the impeller includes aplurality of vanes and a substantially ring-shaped annular connectingmember attached to outer parts of the vanes, and the oblique surface onwhich the driven magnets are fixed is formed on a lower surface of theannular connecting member.

[0017] These and other advantages of the present invention will becomeapparent to those skilled in the art upon reading and understanding thefollowing detailed description with reference to the accompanyingfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a cross-sectional view of a turbo blood pump accordingto an embodiment of the present invention;

[0019]FIG. 2A is a plan view of a rotor of the turbo blood pump shown inFIG. 1 and FIG. 2B is a front view of the same; and

[0020]FIG. 3 is a cross-sectional view of one example of a turbo bloodpump employing magnetic coupling.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021]FIG. 1 is a cross-sectional view of a turbo blood pump accordingto one embodiment of the present invention. In FIG. 1, reference numeral1 denotes a housing, which includes a pumping chamber 2 for passingblood to cause the blood to flow. The housing 1 is provided with aninlet port 3 communicating with the upper part of the pumping chamber 2and an outlet port 4 communicating with the side part of the pumpingchamber 2. Inside the pumping chamber 2, an impeller 5 is disposed. Theimpeller 5 includes six vanes 6, a rotary shaft 7, and a ring-shapedannular connecting member 8. The inner portion of each vane 6 isconnected to the rotary shaft 7 whereas the outer edge thereof isconnected to the annular connecting member 8. The rotary shaft 7 isrotatably supported by an upper bearing 9 and a lower bearing 10, whichare both provided in the housing 1. The annular connecting member 8 isprovided with magnet cases 11, in which driven magnets 12 may beembedded, respectively. The annular connecting member 8 may have sixdriven magnets 12 of a cylindrical shape arranged at predeterminedintervals in its circumferential direction.

[0022] In the lower part of the housing 1, a rotor 13 is disposed. Therotor 13 includes a drive shaft 14 and a magnetic coupling portion 15 ofa substantially cylindrical shape, which are connected with each other.Although it is not shown in the drawing, the drive shaft 14 is rotatablysupported and is rotationally driven by a rotation drive source such asa motor. Further, although it is not shown in the drawing, the rotor 13and the housing 1 are held so that they can keep a constant positionalrelationship. On the upper surface of the magnetic coupling portion 15,driving magnets 16 may be embedded. As shown in a plan view of the rotor13 illustrated in FIG. 2A, six driving magnets 16 of a cylindrical shapemay be arranged at predetermined intervals in the circumferentialdirection.

[0023] The driving magnets 16 are arranged so as to face the drivenmagnets 12 via the wall of the housing 1. Accordingly, the rotor 13 andthe impeller 5 are magnetically coupled with each other. When the rotor13 is rotated, the impeller 5 is rotationally driven through themagnetic coupling.

[0024] As shown in FIG. 1, the lower surface of the annular connectingmember 8 on which the driven magnets 12 are mounted is an obliquesurface, which is not perpendicular to the rotary shaft 7 but inclinesat a predetermined angle. Also, the upper surface of the magneticcoupling portion 15 on which the driving magnets 16 are mounted is anoblique surface. Thus, the driven magnets 12 and the driving magnets 16induce the magnetic coupling on the surfaces that incline with respectto the rotation axis of the impeller 5.

[0025] If the surfaces inducing the magnetic coupling incline asdescribed above, the magnetic attraction force acting between theimpeller 5 and the rotor 13 is induced in the direction inclining withrespect to the rotation axis of the impeller 5. As a result, the loadapplied downward to the lower bearing 10 is reduced. Therefore, thelower bearing 10 suffers with less chance of damage to the bearing,whereby a sufficiently strong magnetic coupling thus can be providedeasily.

[0026] Moreover, as compared with the structure shown in FIG. 3 in whichthe magnetic attraction force acts in the radial direction, an area ofthe portions where the driven magnets 12 and the driving magnets 16 faceeach other, respectively, can be increased without increasing the sizeof the outer peripheral surface of the annular connecting member 8 inthe axial direction because the driven magnets 12 and the drivingmagnets 16 are arranged in the oblique surfaces. Therefore, the size Aof the surface area of the outermost peripheral portions coming intocontact with blood at high peripheral velocity is decreased, therebyreducing the chances of hemolysis. In addition, blood stagnationportions 17 formed between the inner peripheral surface of the annularconnecting member 8 and the wall of the housing 1 are also made smaller,thereby reducing the formation of thrombus.

[0027] The direction of the magnetic coupling is shown in FIG. 2B by thestraight line M perpendicular to the oblique upper surface of themagnetic coupling portion 15. The straight line Y indicates the rotationaxis. An angle α at which the direction M of the magnetic couplinginclines with respect to the rotation axis Y is set in the range of30°±15°. When the angle α is in this range, the effects described abovecan be obtained in a well-balanced state. The angle α greater than thisrange is not preferable because it can bring about a problem as in thecase of the magnetic coupling in the radial direction, i.e., an increasein the surface area of the outer peripheral portions having the highperipheral velocity. Also, the angle α smaller than this range is notpreferable because it can bring about a problem as in the case of themagnetic coupling in the vertical direction, i.e., an increase in theload applied to the lower bearing 10.

[0028] The oblique surfaces preferably are formed so that the magneticcoupling portion 15 of the rotor 13 protrudes upward to form a convexshape. As compared with the case where the magnetic coupling portion 15recedes downward to form a concave shape, the space formed between theoblique surfaces and the impeller 5 can be made smaller, whichcontributes to reducing the size of the pump.

[0029] Further, the diameter of the surfaces of the driving magnets 16facing the driven magnets 12 preferably is greater than that of thesurfaces of the driven magnets 12 facing the driving magnets 16. Inother words, an area of the surfaces of the driving magnets 16preferably is greater than that of the surfaces of the driven magnets12. According to this structure, the torque can be transmittedefficiently through the magnetic coupling.

[0030] When more than twelve driven magnets 12 and driving magnets 16are arranged in the circumferential direction, the spaces between therespective magnets become too close, thereby preventing smooth rotation.Accordingly, it is preferable to arrange four to eight respectivemagnets in the circumferential direction. When the number of the drivenmagnets and the driving magnets is both in this range, the pump canprovide the most beneficial effect with respect to the driving force andthe stability.

[0031] The invention may be embodied in other forms without departingfrom the spirit or essential characteristics thereof. The embodimentsdisclosed in this application are to be considered in all respects asillustrative and not limiting. The scope of the invention is indicatedby the appended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

What is claimed is:
 1. A turbo blood pump comprising: a housing having apumping chamber, an inlet port, and an outlet port; an impellerrotatably disposed in the pumping chamber; bearings for rotatablysupporting the impeller; a rotor provided outside the housing androtationally driven by a motor; driven magnets mounted on the impeller;and driving magnets mounted on the rotor; the driven magnets and thedriving magnets facing each other via a wall of the housing to formmagnetic coupling, rotation of the rotor being transmitted to theimpeller through the magnetic coupling, wherein the driven magnets andthe driving magnets are arranged so that a direction of the magneticcoupling, which is defined based on an attraction force acting betweenthe driven magnets and the driving magnets, inclines with respect to arotation axis of the impeller.
 2. A turbo blood pump according to claim1, wherein an angle at which the direction of the magnetic couplinginclines with respect to the rotation axis of the impeller is in a rangeof 30°±15°.
 3. A turbo blood pump according to claim 1, wherein thenumber of the driven magnets and the number of the driving magnets arein a range of 4 to 8, respectively, and the driven magnets and thedriving magnets are arranged at substantially uniform intervals oncircumferences centered on the rotational axis of the impeller,respectively.
 4. A turbo blood pump according to claim 1, wherein thewall of the housing between the driven magnets and the driving magnetsinclines at a predetermined angle with respect to the rotation axis ofthe impeller, oblique surfaces inclining along the wall are formed in alower part of the impeller and an upper part of the rotor, respectively,and the driven magnets and the driving magnets are arranged on theoblique surfaces, respectively, so as to face each other in parallel. 5.A turbo blood pump according to claim 4, wherein the oblique surface inthe upper part of the rotor protrudes toward the housing so as to form aconvex shape.
 6. A turbo blood pump according to claim 5, wherein theimpeller includes a plurality of vanes and a substantially ring-shapedannular connecting member attached to outer parts of the vanes, and theoblique surface on which the driven magnets are fixed is formed on alower surface of the annular connecting member.